1. Field of the Invention
The invention relates to a spark plug with an insulator, a center electrode placed in the insulator, a casing placed on the outside of the insulator and a casing electrode attached to the casing.
2. Description of Related Art
In spark plugs of the type to which the invention is directed, the center electrode and/or the casing electrode are, usually, made of silver or nickel alloys or of a nickel-copper binary material. Additionally, spark plugs with platinum electrodes as the center electrode and/or casing electrode also are known.
From German Offenlegungsschrift 2 508 490, there is also known a silver-nickel composite material in the form of a silver-nickel fiber composite for electrodes and a process for its production.
In a spark plug with platinum electrodes, large amounts of platinum are needed as erosion reserves for a long lifetime of the spark plug, for example, for gasoline engines, a life of over 1,000 hours. The platinum must further be protected from carbonization, and the high compression pressures in gasoline engines necessitate small electrode gaps. But, small electrode gaps of, for example, 0.3 mm are difficult to establish. The use of platinum metals and platinum alloys for the production of electrodes is further connected with high costs.